Zero is an asynchronous task scheduler that is built upon twisted and interfaces with celery. It is intended to be largely interchangeable with celery's built-in celerybeat scheduler (although that is definitely a work in progress). The biggest difference is that zero runs in a twisted event loop, making it possible to do things such as call web tasks without having to tie up a worker process.
Zero is still in the proof of concept phase.
Zero currently does not support celery's PeriodicTask interface largely due to it working differently from twisted.scheduling's interface. A fix for this is planned. You may make tasks schedulable by subclassing zero.cron.CronTask. Upon doing so, you must give the subclass a cron attribute which has the same syntax as cron. Ex:
class MyTask(CronTask):
cron='*/5 * * * *'
def run(self):
print 'Hello, world!'